1. Field of the Invention
This invention relates to a communication apparatus connected to an ISDN and capable of making a call with a function having a different attribute during communication.
2. Description of the Prior Art
An ISDN (integrated service digital network) has recently been developed as a digital transmission circuit network to make possible a communication service for transmission of images, voice and various other types of information.
With such an integrated service network, a plurality of transmission channels are available. A plurality of terminals such as G4 facsimile machines can be connected to a single subscriber's line, and two or more of these terminals can be operated simultaneously on the user side.
More specifically, in an ISDN, there are two information channels (B channels), which can be used simultaneously. This makes it possible for the user to carry on a telephone conversation while using a facsimile machine (FAX). In such case, the other party on the telephone can also make such simultaneous use of the FAX and telephone to converse while communicating by facsimile.
In a FAX transmission, there are cases where it is desired to contact the sender of a document to verify its contents during reception of the document from the sending party, or where it is desired to supplement a document during transmission of the document to the other party. At such times, the practice in the prior art is for the operator to place a call just as in the case of an ordinary telephone in order to deal with the situations mentioned above. When it is desired to contact the facsimile communicating party during a FAX transmission, so-called dialing (inclusive of push-button operation) is performed during the transmission.
Further, in an ISDN, there are cases where a "change-of service" function is available, in which an attribute is changed (e.g., from image to voice) without disconnecting the call to the other party's machine during a transmission. With an ISDN having this function, it is possible for voice data to be transmitted following the completion of an image data transmission. U.S. Pat. No. 4,995,073 is directed to an invention employing this change-of-service function. However, in order to carry out a separate transmission during the transmission of data, dialing is necessary even if the change-of-service function is used.
Reference will now be had to FIG. 6 to describe a case where a facsimile machine having a telephone function is connected to the abovementioned ISDN to transmit image information on one "B channel" thereof, during which time the other "B channel" is used for a simultaneous telephone conversation.
As shown in FIG. 6, a facsimile machine 61 comprises a call controller 62, an image communication unit 63, a voice communication unit 64 and a communication controller 65. These are connected to an ISDN 70 via line terminating equipment 69. The communication controller 65 controls the data link with the ISDN 70 in accordance with the data link control procedure of the ISDN 70. The call controller 62 administers an incoming/outgoing call protocol to control a "D channel" (Dch) 66 via the communication controller 65. After a call is connected, the image communication unit 63 controls the sending and receiving of image data on, e.g., a "B channel" (B1ch) 67 in accordance with a facsimile transmission procedure. The voice communication unit 64 controls the sending and receiving of voice data on another "B channel" (B2ch).
When the image communication unit 63 is sending or receiving image data on B1ch 67 in the facsimile machine 61 constructed as set forth above, a call procedure must be executed by the call controller 62 if a telephone call is to be made to the other party involved in the communication. If the call is connected, voice data is transmitted on B2ch 68 from the voice communication unit 64 and a conversational state is established.
However, if the communication mode is, say, the reception mode in a case where it is desired to place a telephone call to the same party presently involved in a FAX transmission, a telephone conversation with the sender of the image data cannot take place unless the number of this sending party is entered, irrespective of the fact that the number of the sending party is being received when the call is connected. This is inconvenient. In addition, if the communication mode is the sending mode, it is necessary to dial the same number again even though the other party's number has already been entered in accordance with the transmission procedure. As a result, the calling operation performed by the operator takes time.
Furthermore, if the other party's telephone number is unknown when data is being received from the other party, the operator must take the trouble to look up the number. Moreover, since the act of dialing in the number depends upon the operator, errors are easily made and the wrong number may be dialed.